The relative K-electron capture probabilities (P K ) to the 1383.23, 896.98, 618.09, 442.78 and 322.43 keV levels in 99 Ru in the decay of 99 Rh are measured employing the X-γ internal sum-coincidence technique. The measured values P 1383.23 K = 0.851 ± 0.066, P 896.98 K = 0.834 ± 0.061, P 618.09 K = 0.870 ± 0.01, P 442.78 K = 0.882 ± 0.035 and P 322.43 K = 0.852 ± 0.061 are found to be in good agreement with the theoretical values. The dependence of P K on EC transition energy is discussed.